1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an LCD device capable of enhancing a display quality on a screen by minimizing feature changes of light emitting diodes (LED) due to heat in a structure that heat is rapidly emitted, from the LED serving as a light source, to outside of a lower cover.
2. Background of the Invention
In general, a liquid crystal display (LCD) device is being widely used due to advantages such as a light weight, a thin thickness, and low power consumption. Accordingly, the LCD device is being widely used to display images on screens of a portable computer, a portable phone, and office automation equipment.
The LCD device displays desired images on a screen by controlling optical transmittance according to image signals applied to a plurality of controlling switching devices arranged in a matrix format.
The LCD device comprises an LC panel and a driving portion. The LC panel includes an upper substrate, a color filter substrate facing a lower substrate, a thin film transistor (TFT) array substrate, and an LC layer sandwiched by the upper and lower substrates. The driving portion drives the LC panel by supplying scan signals and image information to the LC panel.
Since the LCD device does not spontaneously emit light, it is provided with a light source to supply light to the LC panel. Accordingly, the LCD device is provided with a backlight assembly including a light source to supply light to the LC panel, a light guide plate for converting light emitted from the light source into white light which is uniformly planarized, an optical sheet, etc.
The optical source of the backlight assembly includes cold cathode fluorescent lamps (CCFL), external electrode fluorescent lamps (EEFL), light emitting diodes (LED), etc.
As an optical source of the conventional backlight assembly, the cold cathode fluorescent lamps (CCFL) were mainly used. However, nowadays, an LCD device mostly adopts the light emitting diodes (LED) having advantages in power consumption, weight, brightness, etc. according to its trend such as a small size, a thin thickness, and a light weight.
Hereinafter, the conventional LCD device will be explained in more detail with reference to the attached drawings.
As shown in FIG. 1, the conventional LCD device comprises an LC panel 1, a plurality of light emitting diodes 2 for supplying light to the LC panel 1, a printed circuit board (PCB) 5 having the light emitting diodes 2 mounted thereon, a lower cover 3 having the PCB 5 fixed to an inner side surface thereof, a light guide plate 6 disposed in the lower cover 3, for guiding light emitted from the light emitting diode 2 to the LC panel 1, an optical sheet 7 for converting light emitted from the light guide plate 6 and supplying it to the LC panel 1, and a reflection sheet (not shown) for reflecting light that has leaked to a lower side of the light guide plate 6 thereby guiding into the light guide plate 6.
The plurality of light emitting diodes 2 mounted on the PCB may be provided with three light emitting diodes, red, green, and blue (RGB) as one unit, so that white light can be emitted as the respective RGB diodes are mixed to each other. The light emitting diodes 2 may be also configured so as to emit white light by being additionally provided with a fluorescent material at exit surfaces thereof.
As the light emitting diodes 2 are used for a long time, light emitted from the light emitting diodes 2 has feature changes. This may cause white light close to one of RGB rather than pure white light, to be supplied to the LC panel 1.
More concretely, the light emitting diodes 2 have disadvantages to generate a large quantity of heat when being driven, whereas they have advantages in power consumption, weight, and brightness, and the RGB light emitting diodes 2 have different feature changes occurring due to heat. Accordingly, as usage time of the light emitting diodes 2 lapses, white light close to one of RGB rather than pure white light, is supplied to the LC panel 1. This may cause the LC panel 1 to display one of RGB on its screen, which may degrade a display quality on the screen.
Accordingly, there have been required means to rapidly emit heat generated from the light emitting diodes 2 to outside of the lower cover 3.